Luminescent (including fluorescent and phosphorescent) markers have a wide variety of applications in science, medicine and engineering. In many cases, these markers provide competitive replacements for radiolabels, chromogens, radiation-dense dyes, etc. However, a significant limitation to the use of luminescent markers is generating an acceptable signal-to-noise ratio. Marker-dependent properties such as absorption and emission maxima, Stoke's shift, quantum yield, etc. affect the ability to distinguish signal from auto- or background fluorescence. Therefore, there is a continuous need to provide improved luminescent markers; especially luminescent markers with long-lived luminescence, and/or a large Stoke's shift with long wavelength emissions. Other useful and desirable properties include: easy and cost-effective synthesis; chemical and thermal stability; convenient attachment to a wide variety of macromolecules including proteins and nucleic acids; efficient excitability; capable of intense luminescence; and the capacity to perform as good luminescent resonance-energy transfer donors.